Precipitating autoantibodies against the ribonucleoproteins Ro/SSA and La/SSB are commonly encountered in systemic lupus erythematosus (SLE) and Sjogren's syndrome (SS). The presence or absence of these precipitating autoantibodies is strongly associated with very different clinical findings and disease subsets. For example, both the systemic manifestations of Sjogren's syndrome as well as most cases of congenital complete heart block are very closely associated with anti-Ro/SSA precipitating antibodies. Our recent work with Ro/SSA and La/SSB has led to their purification and their further molecular characterization and the development of sensitive assays for their respective autoantibodies. Studies with these assays have not only led to better understanding of the human disease processes but also to the demonstration that they are immunogenic in animals. This project will test the hypothesis that the humoral autoimmune responses to Ro/SSA and La/SSB in SLE and SS are restricted. It will be determined whether all or only some of the epitopes of Ro/SSA and La/SSB react with the relevant SLE and SS autoantibodies. This will be done by first developing and applying anti-Ro/SSA and anti-La/SSB sera and monoclonal antibodies from a number of sources. Their capacity to inhibit the SLE and SS anti-Ro/SSA and anti-La/SSB reactivity (and vice versa) will then be determined. Sources of anti-Ro/SSA and anti-La/SSB reagents will include heteroimmune antisera from rabbits and mice and murine monoclonal antibodies, sera from SLE and SS patients, normal individuals with anti-Ro/SSA and anti-La/SSB, human myeloma monoclonal antibodies, and sera from patients (and family members) with C2 deficiency and anti-Ro/SSA. The characterization of each of these sources of reagents will be done in a manner that will permit addressing additional important questions beyond B cell autoimmune repertoire restriction. A study using the anti-Ro/SSA anti-idiotype 6-49 will also be performed with anti-Ro/SSA solid phase assay positive, anti-Ro/SSA precipitin negative patients and normal donors to determine the correlation of this idiotypic marker with anti-Ro/SSA as a potential explanation for B cell repertoire restriction. The proposed biochemical and immunochemical methods of RNA-protein purification, solid phase immunosorbent assays, immunization, hybridoma fusions, cloning, expansion and analysis are all in standard use by the principal investigator's laboratory.